Many polymerization reactions involve the processing of high viscosity materials. For Example, the viscosity of a molten polycarbonate is high, and it is therefore difficult to remove foreign matter from the polycarbonate. It is, furthermore, typically required that new surfaces are constantly generated during the processing of such high viscosity materials, for example, in order to allow evaporation of by-products of the polymerization reaction (such as during the manufacture of a polycarbonate), in order to allow the evaporation of unreacted monomers (such as during the manufacture of polystyrene based materials), as well as in order to achieve a good mixing of all components (inherently achieved when generating the surfaces), or in order to allow a further completion of the polymerization reaction (an example again would be the manufacture of polystyrene based polymers or polycarbonates).
Various types of polymerization reactors have been developed for such processes, involving typically either mechanical agitation of highly viscous reaction mixtures, such as in horizontal twin-screw reactors, or static mixers which utilize gravity to achieve effective surface renewal and the mixing of highly viscous compositions, such as falling-film-evaporators. Examples of such polymerization reactors and processes employing same are disclosed in U.S. Pat. No. 5,932,683 as well as in European patent applications EP 1 760 105 A1, EP 1 760 106 A1, EP 1 760 107 A1, EP 1 760 108 A1 and EP 1 760 109 A1.
However, these conventional approaches towards the processing of highly viscous polymerization compositions have several drawbacks. Polycarbonate resins for example, when produced with twin-screw reactors typically show discoloration and poor stability because of the high shear rates and corresponding high temperature conditions during the processing in the twin-screw reactor. In addition, due to the high viscosity, it is difficult to produce high molecular weight products.
The processes employing reactors utilizing only gravity to achieve effective surface renewal and the mixing of the highly viscous polymerization materials are disadvantageous due to the fact that high retention times are required, decreasing the economic value of such polymerization processes.
U.S. Pat. No. 6,630,563 discloses a process of producing highly viscous polymers using a reactor consisting of rotatable cylindrical baskets having a cylindrical perforated wall and discs positioned along the periphery of the basket. During the process, the reactor is partially filled with the molten reaction mixture. The perforated structures are drawn through the melt by means of rotation, so that once the perforated structures emerge again from the melt, they do provide the possibility for the adhering melt to flow downward in order to produce a continuous film enabling surface renewal.
However, even this process still does not allow a highly satisfactory handling of highly viscous polymerization compositions.